Coffee machines dispensing not only brewed beverages but also milk are known in large numbers, e.g. from DE-A-44 45 436. The known coffee machine comprises a foaming unit with which liquid fresh milk taken e.g. from a separate milk container or from a retail pack, such as the known milk cartons, is heated and foamed with the aid of air and steam introduced in the milk. The milk foam is then used for preparing cappuccino. Fresh liquid milk is, however, perishable and necessitates a cold chain which, for hygienic reasons, should not be interrupted as far as possible. Since the percentage of milk-containing beverages, such as cappuccino, white coffee, latte macchiato, etc., increases constantly, the proportion by volume of milk of the hot beverages dispensed already amounts to more than 60% in many enterprises, such as restaurants, cafes or the like. The large amount of milk to be provided creates problems as regards logistics-transport, stockkeeping, cooling and provision of the milk for the coffee machine as well as additional handling through constant replacement of the milk carton and replenishment. Moreover, additional large-volume cooling facilities are required in the counter area.
However, the known coffee machine also offers the possibility of foaming cold milk or of simply heating the milk making use of the steam so that hot milk can be dispensed. The foaming of cold milk requires a high energy input within the shortest possible time, the heating speed being, however, restricted by physical limits. Providing these large amounts of energy in the form of steam is very costly and necessitates the use of a powerful steam generator or steam boiler, since, at least in some countries, the customers' preference tends towards an increasingly higher percentage of milk or milk foam in comparison with the volume of the rest of the beverage. This has the effect that the time required for preparing hot milk or hot milk foam becomes more and more dominant in comparison with the time required for preparing the beverage so that there will be a substantial increase in the time which is necessary for preparing the whole beverage, and this may cause problems, especially in periods of peak activity in restaurants or the like.